Add histogram stats for send delay for a sent video stream.

webrtc/video/video_send_stream.cc

Index: webrtc/video/video_send_stream.cc
diff --git a/webrtc/video/video_send_stream.cc b/webrtc/video/video_send_stream.cc
index baec5a23d49f3d7feb39e4ba1d90be298d03a9ce..be70662caa3dd9110e27a3cc89a401ec5df21684 100644
--- a/webrtc/video/video_send_stream.cc
+++ b/webrtc/video/video_send_stream.cc
@@ -64,6 +64,7 @@ std::vector<RtpRtcp*> CreateRtpRtcpModules(
   configuration.send_bitrate_observer = stats_proxy;
   configuration.send_frame_count_observer = stats_proxy;
   configuration.send_side_delay_observer = stats_proxy;
+  configuration.send_packet_observer = stats_proxy;
   configuration.bandwidth_callback = bandwidth_callback;
   configuration.transport_feedback_callback = transport_feedback_callback;
 
@@ -704,6 +705,10 @@ void VideoSendStream::OnBitrateUpdated(uint32_t bitrate_bps,
   vie_encoder_.OnBitrateUpdated(bitrate_bps, fraction_loss, rtt);
 }
 
+bool VideoSendStream::OnSentPacket(int packet_id) {
+  return stats_proxy_.OnSentPacket(packet_id);
+}
+
 int VideoSendStream::ProtectionRequest(const FecProtectionParams* delta_params,
                                        const FecProtectionParams* key_params,
                                        uint32_t* sent_video_rate_bps,